Automatic control system for sewing machines

ABSTRACT

An automated control system for a sewing machine which includes a stepping motor for pulsatingly feeding the work material into the path of the sewing head needle assembly and control means for driving said stepping motor in response to programmed instructions preset by the operator at the outset of the sewing operation. The control means preferably comprises digital logic circuitry which generates control pulses for the stepping motor to govern stitches per inch and back tack.

United States Patent Kamena 5] Apr. 11, 1972 [54] AUTOMATIC CONTROL SYSTEM FOR 2,970,557 2/1961 Schwab et al ..112/121.11 SEWING MACHINES 3,074,632 l/l963 Braun et a1 ..1 12/121.1 1 x 3,329,109 7/1967 Portnotf et a1 ..112/204 X [721 Invent Dav"! Kama", 3,385,244 5/1968 Ramsey et al ..1 12/121 12 [73] Assignee: Pneumatic Systems Inc., New York, NY.

. Primary Examiner-James R. Boler [221 1969 Attorney-Eugene Lieberstein and Gerald Weir [21] Appl.No.: 848,998

[57] ABSTRACT U.S. 3 An automated ontrol ystem for a sewing machine which in- [5 Cl. cludes a Stepping motor for pulsatingly feeding the work [58] Fleld of Search ..1 12/2, 121.1 1, 121.12, 121.15, i l into the path of the Sewing head needle assembly and 1 12/204' 102; 318/696 control means for driving said stepping motor in response to programmed instructions preset by the operator at the outset [56] References cued of the sewing operation. The control means preferably com- UNITED STATES PATENTS prises digital logic circuitry which generates control pulses for the stepping motor to govern stitches per inch and back tackv 1,942,128 1/1934 Sommer ..112/l2l1l5 2,906,217 9/1959 Myska ..1 l2/l2l.11 9 Claims, 8 Drawing Figures on 62 r flca" i 57 5.9 lMAGNETIC l I l anta l l 1 L2 1 FEE-JACK RUNNlNG TACK POST TACK TC CWER SOURCE.

PEDAL CONTROL PATFNTEDAPR 11 I972 3, 654, 882

sum 1 or a STITCH PEINCH RUNNING TACK PPERTT@-)CK POST 100 10 UNITS W. WI" '11,) BNVENT m DAVID H. NANA PATENTEDAPR 11 1972 3, 654, 882

SHEET 2 BF 4 STITCHES PER INCH ERE TACK 10 @L I @1: I START 7 s |O|111 21 a 5'] I POST TACK |i INVENTOR (3,757.5 DAVID H. KAMENA ATTORNEY PATENTEDAPR H 1972 3. 654, 882

SHEET 0F 4 (EATING MATRIX W ullmml HIHW H nmulln .200 44 H il II I umnmlllll lllllllll INVENTOR DAVID H. KAME BY g: 5 ATTORNEY AUTOMATIC CONTROL SYSTEM FOR SEWING MACHINES This invention relates to sewing machines and more particularly to an automated control system for an industrial sewing machine which provides accurate adjustable control of the stitch-length and back-tack.

Sewing machines of present day design perform the forward feeding and back-tack operations by mechanical means. Stitch-length is controlled by eccentrically positioned cams whose eccentricity may be adjusted by a mechanical linkage for varying the stitch-length. Variations in cam eccentricity affect stitch regularity and evenness, thereby limiting the degree of effective control over stitch length to within a narrow range for any given drive cam design. Moreover, such systems are unwieldy, wear relatively quickly and with age the stitches under the control of a mechanical system become less uniform. In addition, it is difficult to independently and automatically control back-tack with any reasonable degree of effectiveness and near to impossible with conventional mechanical systems to adjust the leading or pre-tack stitch-length separately from that of the trailing or post-tack stitch-length while maintaining a fixed rate of stitches per inch. For purposes of the present disclosure back-tack" refers to the locking stitches at the leading and trailing edges of the material while pre-tack refers specifically to the locking stitches at the leading edge and post-tack to the locking stitches at the trailing edge. It is further intended for purposes of the present disclosure to refer to the forward feeding stitches over the entire sewn length as the running-tack.

The control system of the present invention overcomes all of the above shortcomings in conventional mechanically controlled industrial sewing machines. The sewing material is fed electromechanically by means of a stepping motor which is in turn digitally controlled in accordance with preestablished instructions preset by the operator at the outset of the sewing operations or, if desired, programmed into the control system.

It is therefore the primary object of the present invention to provide a new and improved nonmechanical control system for a sewing machine which for a given control setting automatically controls the number of stitches per inch and which further provides independent adjustable back-tack control at the preselected rate of stitches per inch.

Another object of the present invention is to provide a control system wherein the stitches per inch rate may be varied over an appreciably wide range.

It is a further object of the present invention to provide a control system for a sewing machine for automatically performing a pre-tacking operation at the leading edge of the material being sewn and a post-tacking operation at the trailing edge of the material being sewn wherein either the number of stitches or the stitch length at the leading and trailing edges respectively may be selectively varied.

It is a still further object of the present invention to provide a control system for a sewing machine wherein the operator can selectively program the desired number of stitches per inch, and the number of stitches for each of the pre-tact, posttact, and running-tack operations respectively, which operations will be automatically performed by the sewing machine.

It is yet a further object of the present invention to provide a control system for a sewing machine wherein the pre-tact, post-tact, and running-tack operations respectively are synchronized to the stroke of the sewing needle such that the material to be sewn is advanced past the needle only when the needle is out of work material.

These and other objects and advantages will become apparent from the following description and the accompanying drawings of which:

FIG. 1 is a diagrammatic view of the sewing machine of the present invention and a perspective view of the operators control panel.

FIG. 2 is a diagrammatic representation of the sewing machine illustrating the relationship of the sewing head and table assembly for performing a sewing operation.

FIG. 3a is an enlarged view of the sensing means and tooth assembly of FIG. 1.

FIG. 3b is an illustration of an output signal generated by the sensing means of FIG. 3a for a full revolution of the tooth.

FIG. 4 is a schematic logic diagram of the control circuitry of the present invention.

FIG. 5 is another perspective view of the operators control panel illustrating an alternate embodiment of the invention.

FIG. 6 is a diagrammatic representation of the alternate embodiment for controlling back-tack.

FIG. 7 is a top plan view of the drive assembly of FIG. 2 illustrating the relationship between the drive assembly and the synchrotransmitter for the alternate embodiment of the invention.

Referring more particularly to FIGS. 1 and 2 in which a typ ical sewing machine 10 is shown including a frame comprising a bed 12 from one end of which rises a hollow standard 14 of a tubular bracket arm 16 overhanging the bed 12 and terminating at its free end in a hollow head 18. Bracket arm 16 carries drive shaft 20 which is rotatably driven by a conventional flywheel clutch drive assembly 22 symbolically illustrated in FIG. 1 and controlled through a foot pedal 24. Set to reciprocate in head 18 is a needle 26 which is responsive to the rotation of drive shaft 20. Conventional shuttle and bobbin case are not shown. A pair of cutting knifes 21 activated at the end of the sewing operation for cutting the connecting thread between the needle and work material are shown in block form located directly beneath base plate 27 in line with needle 26.

Machine bed 12 supports, in a substantially horizontal position, base plate 27 upon which is mounted a sliding table 28. Sliding tale 28 is flanged at one end to form an open ended generally rectangular channel 30, the open end of which is seated in guide rail 31 of base plate 27 for restricting sliding table 28 to longitudinal movement with respect to the machine bed, as shown by the arrows in FIG. 2. Alternatively, channel 30 may be separately fabricated and attached to the otherwise flat sliding table 28. A fabric clamp 32 is pivotally connected to channel 30 on one side thereof and extends outwardly therefrom to form a flat base section 34 located beneath the sewing needle 26. Section 34 of clamp 32 is slotted lengthwise as shown in FIG. 2 to permit needle 26 to pass therethrough during the sewing operation. A piece or strip of fabric is positioned by the sewing operator between clamp 32 and sliding table 28 before the sewing operation is started in a manner to be more fully described hereafter. Clamp 32 is preferably actuated by a solenoid 35 shown schematically in FIG. 4 for engaging or disengaging the flat base section 34 of clamp 32 into or from direct contact with the sliding table 28. The solenoid 35 may be housed in the barrel portion 36 of clamp 32.

Channel 30 of sliding table 28 is longitudinally advanced in incremental steps by a drive motor M through a drive unit assembly 42. Drive unit assembly 42 consists of a pully 44 rotatably connected to the shaft of drive motor M and a timing belt 46. The timing belt 46 may be fixedly attached to channel 30 by bonding it thereto or engaged therewith in a pinionrack relationship. In the latter case gear-like teeth would be required on both the inside and outside track of timing belt 46 and on the side of channel 30 adjacent thereto. Although a timing belt and pully arrangement is preferred for controllably advancing sliding table 28 in response to the rotation of drive motor M, any known conventional drive means may be used.

Drive motor M for purposes of this invention may be of any conventional type which may be driven in alternate directions in response to discreet control signals or pulses. However, it is preferred to select motor M from the class known to the art as stepping motors. A stepping motor is generally of the permanent magnet synchronous type having polyphase bifilar field windings. The shaft of the stepping motor is caused to make a discreet rotational step for every pulse applied to the field windings. The field windings are energized in an appropriate sequence by steering circuitry which controls the direction of motor rotation. The steering circuitry conventionally referred to as a translator is not part of the present invention and is therefore not shown. The only requirement in the choice of stepping drive motor M is that it be capable of incrementally advancing sliding table 28 in response to each discreet control signal applied thereto. Thus, the sliding table 28 will be advanced in predetermined increments in either longitudinal direction as shown by the arrows in FIG. 2 in response to the control signals applied to drive motor M.

The control signals applied to drive motor M are generated from the operator's control panel 50 illustrated in FIG. 1. A number of manually adjustable control dials representing rotary switches are shown on the face of the control panel 50. The control dials are identified in accordance with their functions, i.e., stitches/inch, running tack (in hundreds, tens and units), pre-tack and post-tack respectively. Except for the stitches per inch control, each control dial is set to automatically provide a predetermined number of stitches.

Although the motor control pulses for advancing sliding table 28 may be generated independent of the needle drive it is preferred to have the needle drive and material feed drive synchronized. Not only is this important to prevent the needle from bending or breaking due to the movement of the material before the needle has been withdrawn but also permits the formation of controlled stitch patterns.

The sewing needle 26 of sewing machine is reciprocated by the rotation of drive shaft at a substantially constant speed, penetrating the material and returning to rest for each complete revolution of the drive shaft. Sensing means 52 mounted in tubular bracket am 16 generates a synchronizing or clock pulse in response to each revolution of drive shaft 20. Sensing means 52 consists of a pick-up coil which is magnetically coupled to a tooth 56 connected to drive shaft 20. The relationship between sensing means 52 and tooth 56 is more clearly shown in FIG. 3a. As the drive shaft 20 is rotated through 360 the tooth 56 will cross flux lines generated by sensing means 52 to produce an output signal as is shown in FIG. 3b. The tooth 56 is joined to a bearing member 58 which may be rotatably adjusted on drive shaft 20 to insure that the signal generated in sensing means 52 occurs during the upstroke of the needle, i.e., when the needle is out of physical contact with the fabric. Although a clock signal or pulse is developed in response to the needle stroke by means of magnetic intercoupling any other means such as photocell detection may be employed for this purpose. The magnitude of the generated clock signal depends upon the distance between the pick-up coil and the tooth, the magnetic material used, etc. and the speed of the drive shaft. As is shown in FIG. 3b the clock signal generated in the pick-up coil of sensing means 52 goes initially positive and then negative. The clock signal is applied to logic circuitry in the operators control panel 50 which generates in response thereto a predetermined number of control pulses in accordance with the programmed instructions set by the sewing operator as will be hereinafter explained in connection with the schematic logic diagram of FIG. 4.

The control system of the present invention is basically composed of digital logic circuitry which operates in synchronism with the clock pulses generated by sensing means 52. Individually, each circuit is conventional and may employ relays, vacuum tubes, solid state devices or other components I to carry out its functions. Although the electronic logic circuitry to be described is preferred, other conventional logic circuits may be used. Moreover, it is to be understood that the logic functions can be carried out using other techniques which need not be electronic and can, in fact, embrace pneumatics, hydraulics, fluidics, etc.

Circuits 57 and 59 symbollically represent wave shaping circuits which convert the clock signal generated by sensing means 52 into discreet output pulses having a predetermined amplitude and duration. In this regard, block 57 may represent a schmitt trigger and block 59 a monostable multivibrator. The schmitt trigger 57 responds to the positive going part of the clock signal for generating an output pulse to the monostable (one-shot) multivibrator 59 which in turn generates a pulse of predetermined amplitude and duration. The negative going part of the clock signal reverts the schmitt trigger back to its original state. For purposes of simplicity all signals will be hereinafter represented by their binary state, i.e., by either of two voltage levels representing the binary l and 0 respectively. Binary 1 or 0 depending upon the type of logic can represent high or low, positive or negative.

The output of the monostable multivibrator 59 is fed to the set terminal of flip flop 60. The symbols on flip flop 60 designate the following:

S Set C Clear or reset T Toggle l Normally low" state 0 Nomially high state Once the flip flop 60 is set the 1 terminal output represents high and remains in this state until the flip flop is reset by a pulse to the clear terminal. The 1 terminal output of flip flop 60 is applied simultaneously to monostable multivibrator 62 and to and gate 64. The output of oscillator 66 is fed as a second input to the and gate 64. An and gate produces an output signal when there is a time coincidence of all inputs. Oscillator 66 is a free running oscillator generating repeated pulses at a predetermined frequency of approximately 15 times the clock pulse output rate of monostable multivibrator 59. As long as flip flop 60 is set, and gate 64 will pass the pulses generated by oscillator 66 to the stitch length counter 68 which determines the rate of stitches per inch. The stitch length counter 68 is initially cleared by the output of monostable multivibrator 62 and then counts consecutively each output pulse of and gate 64 until a predetermined count is reached in accordance with the setting of the stitches per inch dial on the operators instrument panel 50. Upon reaching the desired count a reset pulse is generated and applied to the clear terminal of flip flop 60. The output of and gate 64 is additionally applied to and gates and 82 of gating matrix 73 for driving motor M in either a forward or reverse direction. Other inputs to the gating matrix 73 control the sequencing and period of motor operation for each direction as will be further explained in more detail later on. Hence, the number of steps taken by motor M for each clock pulse generated by sensing means 52 is determined by the stitch length counter 68 which is in turn controlled by the stitches per inch rotary dial on the operators instrument panel 50. The fewer the steps advanced by motor M for each clock pulse generated by sensing means 52 the greater the number of stitches per inch, i.e., fine stitching and vice versa.

The stitches per inch rotary dial on the operator's instrument panel 50 is calibrated to provide 6-l6 stitches per inch in increments of two omitting the rate of 14 stitches per inch. The exact number of steps required by motor M to provide the desired stitches per inch rate depends upon the selection of motor M and the drive assembly. For a pully type drive arrangement as shown in FIG. 2 and a motor M which steps 18 for every control pulse applied thereto the following approximate correllation is established between steps and stitches per inch where each step of motor M is designed to advance sliding table 28 0.02 inch in either longitudinal direction.

Stitches Per Inch St 6 8 8 6 l0 5 l2 4 l6 3 zero except for one flip flop which stores a l As input pulses occur, the 1 state is moved from memory cell to memory cell in a closed chain or ring. Separate output leads from each flip flop in the ring counter is connected to separate selector points on the rotary switch representing stitches per inch with the wiper arm of the rotary switch connected to an output flip flop. The ring counter and output flip flop would comprise the stitch length counter 68. The wiper arm is set by the sewing operator to the selection point representing the desired number of stitches per inch. The input pulses from oscillator 66 enter the stitch length counter 68 via and gate 64 advancing consecutively the state of each flip flop until a "1 occurs at the chosen selector point of the rotary switch. The l is transmitted via the wiper arm of the rotary switch to the output flip flop of stitch length counter 68 which in turn transmits a reset pulse to flip flop 60 closing and gate 64 before the next pulse arrives from the oscillator 66.

The clock or synchronizing pulses generated in sensing means 52 after passing through wave shaping circuits 57 and 59 are simultaneously applied via lead 70 to the pre-tack, running-tack and post-tack logic circuitry identified and blocked off with dotted lines in FIG. 4 for controlling the direction and period of rotation of motor M in accordance with the instructions set by the sewing operator on the operators control panel 50.

The pretack logic circuitry consists essentially of a pretack counter 72 and an output flip flop identified by the capital letter A. The pretack counter 72 is preferably a simple ring counter which counts in a one out of n mode in a similar manner as hereinbefore described with respect to the stitch length counter 68. For a maximum of nine pre-tack stitches, five cascaded flip flops connected in a logical ring formation would suffice as the pretack counter 72. A pretack rotary switch labeled PRT represents the pre-tack dial on the operators control panel 50. The wiper arm of the pre-tack rotary switch PRT is connected to the toggle input of output flip flop A. Flip flop A is a conventional J-K flip flop which has a normally low l output and a normally high 0 output. A toggle input complements the output. The l output is applied to an inhibitory and gate 74 which also receives as an input thereto the clock pulses via lead 70. The output of and gate 74 is connected to the pretack counter 72. Inhibitory and gate 74 performs a logical and not operation, i.e., the output thereof will be high provided the input 1 from flip flop A is low. Hence, each clock pulse applied to inhibitory gate 74 via lead 70 will be transmitted to the pretack counter 72 until the counter 72 reaches the count designated on the pretack rotary switch PRT as set by the operator. Upon reaching the desired count flip flop A will receive a toggle input complementing its output and disabling inhibitory and gate 74. The 1 and 0 outputs of flip flop A are connected to the gating matrix 73 for controlling the initial direction of motor rotation and the number of pretack stitches to be introduced into the work material.

The running tack logic circuitry comprises a running tack counter 76 which may represent a conventional three stage binary counter and three output flip flops B, C and D representing respectively the output of each state of the binary counter. The three stages are made up of a units-stage, a l0s stage and a l00s stage pennitting a maximum count of 999. A 1,000s stage may be added if a larger count is desired. The three rotary switches labeled RT RT and RT, represent respectively the units, l0s and l00s dial on the operators control panel 50. Inhibitory and gate 78 passes the synchronizing pulses generated from sensing means 52 to the units stage of running tack counter 76 after the pre-tack count has been completed. Output flip flops B, C and D are all conventional J-K flip flops exhibiting a normally low l output and a normally high 0" output. The normally high 0 output of flip flop C is fed back to the clear terminal of flip flop B and the normally high 0 output of flip flop D is fed back to the clear terminal of flip flop C. As is well known to those familiar with logic circuitry a high input to the clear terminal of a J-K flip flop will prevent the toggle input from complementing the output.

Hence, flip flop B cannot reverse its output stage until the output of flip flop C is reversed which in turn requires the output of flip flop D to reverse state. As long as the l terminal of flip flop B remains low and gate 78 will continue to pass the synchronizing pulses from lead 70 to the running tack counter 76. Thus, synchronizing pulses will cycle through the units stage, the 10s stage and the 100s stage until the desired count is reached. The units stage counts each pulse while the 10s stage advances only on each 10th pulse and the 100s stage on each 100th pulse. The scale on each of the three rotary switches RT RT and RT respectively, is adjustable from 0-9. Assuming, for example, the sewing operator desires to make 347 running stitches, the operator would set the 100 dial to 3, the 10s dial to 4 and the units dial to 7. Let us also assume that the pretack operation has just been completed such that the output of flip flop A has reversed. And gate 78 is now prepared to deliver the synchronizing pulses to running tack counter 76. After receiving 300 pulses the 100s stage will deliver an output signal to the toggle input of flip flop D reversing the output thereof and removing the high from the clear terminal of flip flop C. Upon receipt of 40 additional pulses the 10s stage will supply a toggle input to flip flop C, complementing its output and removing the high from the clear terminal of flip flop B. The units stage will then count the next seven pulses and apply a toggle input to flip flop B the output of which will now reverse since the high has been removed from its clear terminal. As soon as the l output of flip flop B turns high and gate 78 is disabled preventing any further delivery of synchronizing pulses to running tack counter 76. The operation of a counter of this type is well known to those skilled in the electronic arts.

The post-tack logic circuitry is substantially identical to the pretack logic circuitry. A post-tack rotary switch labeled PTO represents the post-tack dial on the operators instrument panel 50. The post-tack counter 84 may consist of a simple ring counter, the operation of which would be substantially identical to the operation of the pretack counter 72. Output flip flop E receives a toggle input complementing its output when the post-tack counter reaches the count set by the operator on the post-tack rotary switch PT. Flip flop E is a conventional J-K flip flop, the 1 terminal of which is normally low. inhibitory and gate 86 will pass synchronizing pulses to the post-tack counter after the running tack count has been completed.

The period and sequence of rotation of motor M is determined by gating matrix 73 which receives simultaneous inputs from the pretack, running tack, post-tack and stitches per inch circuits, respectively. Gating matrix 73 comprises logical and gates 80 and 82 and a logical or gate 85. The control pulses passed through and gate 64 from oscillator 66 are applied directly to both and gates 80 and 82. And gate 80 receives two additional inputs, namely, the l output of flip flop A and the 0 output of flip flop B. The 0" output of flip flop E is applied directly to and gate 82 while the 0 output of flip flop A and the l output of flip flop B are applied to and gate 82 through or gate 85. When and gate 80 is enabled motor M is driven in a forward direction. Enabling and gate 82 will cause motor M to be driven in the reverse direction. For purposes of simplicity the following nomenclature will be adopted:

Let:

E representing flip flop E the output stage of the post tack counter 84.

When: 1

the pretack count is complete A will be high;

the running tack count is complete B will be high; the post tack count is complete E will be high.

At the start of the sewing operation, A, B and E will be low. Hence, and gate 80 will be off while and gate 82 will be on since NOT A and NOT E are present. Therefore, motor M will be driven initially in the reverse direction until the pretack count is reached at which time and gate 82 will turn off. Since A is now present and gate 80 will turn on and motor M will be driven in a forward direction. When the preselected running tack count is reached, B will become present turning off and gate 80 and turning on and gate 82 which causes the direction of motor M to reverse again to the initial direction and continue until the post-tack count is reached at which time E is present. When E is present both and gates 80 and 82 are off and the motor M is momentarily halted.

In an alternate manner flip flops A, B and E representing respectively the output stages of the pre-tack, running tack and post-tack counters may be energized directly in response I to stitch length instead of a numerical stitch count. To accomplish this the counting circuitry described heretofore and shown in FIG. 4 would be replaced by an array of photocells. The photocells would be slidably connected to machine bed 12 in proximity to and facing the timing belt 46 of drive assembly 42. A light source would be coupled to the timing belt for movement therewith. The sewing operator would line up the photocells such that their positions coincided with the desired stitch pattern for the work material. As the light source passes each photocell, an electrical circuit would be completed energizing flip flops A, B and E in the same sequence as discussed with respect to the counter circuitry. Hence, gating matrix 73 which governs the direction of stepping motor M would be controlled by stitch length instead of a predetermined number of stitches.

For remote operation, the photocell array may be mounted directly on the operators control panel 50 as shown in FIG. 5. Each photocell is identified by its function. The stitch per inch selector switch controls the rate of stitches per inch as discussed earlier with reference to FIGS. 1 and 4. Each photocell is mounted by means of a tab or clip (not shown) to panel 50 permitting easy manual positioning along scale S. A corresponding scale (not shown) is located on machine bed 12. Hence, the position of each photocell with respect to scale S is equivalent to a given position on the corresponding machine bed scale.

Flip flops A, B and E would be energized by the photocell array in a manner illustrated in the functional schematic diagram of FIG. 6. A synchro transmitter 200 is mounted on the machine bed 12 (not shown) with its shaft coupled to a pully which in turn intermeshes with timing belt 46 of drive assembly 42 as shown in FIG. 7. Timing belt 46 is driven by stepping motor M in response to the operation of stitch length counter 68 as discussed hereinbefore in connection with FIG. 4.

A synchro receiver 202 is electrically connected to the synchro transmitter 200. The shaft of receiver 202 is caused to follow the transmitter shaft in a one to one relationship. Synchro receiver 202 is mounted in control panel 50 with its shaft coupled to a pully for advancing a timing belt assembly (not shown); the arrangement being similar to the assembly shown in FIG. 7. A light source 206 is connected to the timing belt assembly facing the photocell array as shown in FIG. 6. A light shield 208 channels the light generated by light source 206 such that the generated light impinges only on the photocell in line with the light source.

The sewing operator slides the photocells which are mounted on clips in a manner similar to setting tabs on a typewriter. The photocells are set in position to provide the desired lengths of pre-tack, post-tack and running tack, respectively. Stepping motor M will be driven in response to the stitch length counter 68 initially in the reverse direction which in this case will be toward the pre-tack photocell. As soon as light is incident upon the pre-tack photocell, flip flop A receives a toggle input complementing its output. The applied signal to the toggle input is derived from a power supply (not shown). The output of flip flop A is connected to gating matrix 73 as shown in FIG. 4. When the l terminal thereof goes high stepping motor M reverses direction. This reverses the direction of the synchro transmitter 200 reversing the rotation of synchro receiver 202 and causing light source 206 to advance in the forward direction until light is incident on the stop photocell. Although the post-tack photocell precedes the stop photocell and gate 208 cannot pass a signal until flip flop B is complemented. When light impinges on the stop photocell a signal is applied to the toggle input of flip flop B rendering the 1" terminal output thereof high. The direction of stepping motor M is again reversed by gating matrix 73 causing light source 206 to move in the reverse direction toward the post-tack photocell. When light is now incident upon the post-tack photocell flip flop E receives a toggle input complementing its output at which time gating matrix 73 momentarily halts stepping motor M.

SEWING OPERATION At the start of a particular sewing operation, the operator activates sewing machine 10 by flipping an on-off switch 11 located on the instrument panel 50 to the on position. The drive assembly 22 shown only in block form includes a flywheel for rotating drive shaft 20 as is well known in the art. The clutch mechanism itself is conventional and is controlled through a pair of solenoids identified as the start solenoid 100 and the stop solenoid 102 shown schematically in FIG. 4. The two solenoids 100 and 102 are in turn controlled as will be explained hereinafter.

Power is derived from a conventional 115 volt line source through a common power supply which is fed by common bus lines (not shown) to all of the control circuitry. Foot pedal 24 includes two micro-switches and 92 shown in FIG. 4 which are activated sequentially in response to applied foot pressure by the operator. Micro-switch 90 is normally open while micro-switch 92 is normally closed. As soon as machine 10 is activated by the operator, power is supplied through normally closed micro-switch 92 to the and gate 94. A second input to and gate 94 is derived from the 0 terminal of flip flop 96. Flip flop 96 is identical in kind to the flip flops discussed heretofore in connection with the control counter circuitry. Until a pulse is received on the set terminal S of flip flop 96, the 0 terminal is high. Thus, coincident signals are applied to and gate 94 as soon as the operator switches on machine 10 energizing solenoid 35 which in turn draws clamp 32 into the up position shown in FIG. 1. The power amplifier 97 increases the signal output level of and gate 94 for adequately energizing solenoid 35.

The pieces of material to be sewn are positioned by the sewing operator on sliding table 28. A seam will be made in the material which lies directly above an elongated slot in the sliding table 28 and base plate 29. The sewing operator then commences to apply foot pressure to the foot pedal 24. When the pedal is depressed half way down normally closed microswitch 92 is opened. Solenoid 35 is thereby deenergized releasing clamp 32, the base section 34 of which grips the fabric into tight engagement against the sliding table 28 leaving only the material under the slotted area exposed. The operator continues to apply pressure to foot pedal 24 until it is depressed completely down at which time normally open microswitch 90 closes. Power is now applied to the set terminal of flip flop 96 removing the high from the 0" output. In addition, power is supplied to monostable multivibrator 98 which generates a pulse of predetermined amplitude and duration. The pulse is applied to clear the pretack, running tack and post tack counters respectively. Power is also supplied to start solenoid 100 through time delay circuit 104, monostable multivibrator (106) and power amplifier 108. The time delay is required to insure that start solenoid 100 is not energized before the counters are cleared. The start solenoid 100 need only be energized for a time sufficient to engage the motor drive to the fly-wheel of drive assembly 22. Once engaged the fly-wheel can only be disengaged by energizing the stop solenoid 102.

Drive shaft 20 will now be continuously driven by drive assembly 22 until the complete sewing operation is completed. Assuming the ratio between the needle drive and drive shaft is one to one each rotation of the shaft will equal one sewing stitch. The stitches per inch rate will be determined at the outset by the setting on the operator's instrument panel 50 as discussed earlier. The direction of rotation of stepping motor M, which drives sliding table 28 rectilinearly, is controlled by the pretack, running tack and post tack operations respectively which are in turn preset by the operator prior to commencement of the sewing operation.

POST SEWING CONTROL The post sewing control circuitry is shown schematically in FIG. 4. When the post tack count is complete flip flop E will reverse its output rendering the 1 terminal high. The 1" terminal of flip flop E is connected to stop solenoid 102 through a conventional monostable multivibrator 110 and power amplifier 112. As soon as the l terminal of flip flop E goes high, monostable multivibrator 110 applies a pulse of predetermined duration to the stop solenoid 102 which disengages the fly-wheel from the motor drive of drive assembly 22 in a conventional manner. The sewing cycle is then terminated by severing the connecting thread between the needle and the work material. The sliding table 28 is then automatically returned to its initial position and the clamp 32 is released.

To complete the sewing cycle, cutting knives 21 are extended to sever the connecting thread between the needle 26 and the work material. The cutting knives 21 are maintained in a retracted position throughout the sewing operation by solenoid 120. Solenoid 120 receives an energizing signal during the entire sewing cycle from not circuit 122 which is amplified by power amplifier 124. When the l terminal output of flip flop E goes high, monostable multivibrator 116 receives an input signal after a fixed time delay as determined by time delay circuit '114. The output of monostable multivibrator 116 is fed to not circuit 122 and to solenoid 118 through power amplifier 126, when not circuit 122 receives an input its output inverts deenergizing solenoid 120. As the same time solenoid 118 is now energized pulling out cutting knives 21 to an extended position for severing the last stitch.

Simultaneously, the 1 output terminal of flip flop E applies a signal vto return-home oscillator 128 and gate 138 and to a second time delay circuit 130. A not-home microswitch identified by the numeral 132 is maintained in a normally open position when the sliding table 28 is in a predetermined staring or home position. As soon as the sewing operation is started and the sliding table is moved micro-switch 132 closes. In the alternate photocell embodiment micro-switch 132 may be an equivalent electrical switch which is open when the light source is in line with the start photocell. Once the sliding table is moved the switch will close. After a fixed time period as determined by time delay circuit 130 and gate 134 is turned on." Pulses from oscillator 128 are applied through and gate 134 to the reverse terminal of stepping motor M'at a fixed rate. When sliding table 28 reaches its home position micro-switch 132 opens closing and gate 134 and removing the input to not circuit 136. And gate 138 now receives coincident input signals and applies a signal to the clear terminal of flip flop 96 reestablishing its initial condition, i.e., high at the 0 terminal. Assuming the foot pedal 24 has been released solenoid 35 will again be energized lifting clamp 32 back into its original up position. The sewing operation may now be restarted.

What is claimed is:

l. A control system for a sewing machine including a sewing head having a sewing needle and drive means, comprising:

a. means for generating an output signal in response to each stroke of the sewing needle;

b. means for generating a repetitive train of drive signals at a predetermined frequency;

c. manually adjustable counting means for consecutively counting a predetermined number of said drive signals in response to each output signal, said counting means providing an output at the end of each counting cycle;

d. a stepping motor responsive to said drive signals for pulsatingly advancing work material into the path of said sewing needle; and

e. gating means responsive to the output of said counting means for inhibiting said drive signals whereby the distance traversed by said work material for each stroke of the sewing needle is determined by the predetermined number of counted drive signals in each counting cycle.

2. A system as defined in claim 1 further comprising: means for generating a plurality of command signals in response to a sequence of predetermined number of drive signals; and logic circuit means responsive to said command signals for selectively directing said drive signals to said stepping motor such that the direction of advancement of said work material is controlled by said command signals.

3. A system as defined in claim 2 wherein said means for generating said command signals comprises manually adjustable electronic counting means.

4. A sewing machine control system as defined in claim 14 further comprising, a substantially fiat bed, a sliding table mounted on said flat bed, means for clamping the work material to be sewn against said sliding table and means for coupling said stepping motor to said sliding table such that said sliding table is advanced rectilinearly in response to the rotation of said stepping motor.

5. Apparatus as defined in claim 4 wherein said clamping means is pivotally connected to one end to said sliding table for movement therewith and extends outwardly forming a flat base for biasing the work material against said sliding table, and wherein said coupling means comprises a pully and belt drive.

6. A control system for a sewing machine including a sewing head having a sewing needle and drive means, comprising:

a. means for generating a predetermined number of drive signals in response to each stroke of the sewing needle;

b. a stepping motor responsive to said drive signals for pulsatingly advancing work material into the path of said sewing needle;

c. a plurality of light sensitive devices arranged in a predetermined sequence;

d. a light source;

e. means for advancing said light source past each of said light sensitive devices; and

f. gating means electrically connected to each of said light sensitive devices and responsive to the electrical state thereof for alternately changing the direction of travel of said stepping motor such that the distance traversed by said material in each direction is governed by the relative displacement between said light sensitive devices.

7. A system as defined in claim 6 wherein said plurality of light sensitive devices comprises a first photocell representing length of pre-tack, a second photocell displaced a predetermined distance from said first photocell representing length of running tack, and a third photocell displaced a predetermined distance from said second photocell representing post-tack and wherein the position of each photocell with respect to one another is manually adjustable.

8. A system as defined in claim 7 wherein said light sensitive devices are mounted on a panel in a remote location from said sewing machine and wherein said light source is mounted on a movable conveyor adjacent said light sensitive devices.

9. A system as defined in claim 9 further comprising; a substantially flat bed, a sliding table mounted on said flat bed, means for clamping the work material to be sewn against said sliding table, means for coupling said stepping motor to said sliding table such that said sliding table is advanced rectilinearly in response to the rotation of said stepping motor, means for transmitting electrical signals responsive to the movement of said sliding table, and receiving means connected to said movable conveyor in said remote location for 

1. A control system for a sewing machine including a sewing head having a sewing needle and drive means, comprising: a. means for generating an output signal in response to each stroke of the sewing needle; b. means for generating a repetitive train of drive signals at a predetermined frequency; c. manually adjustable counting means for consecutively counting a predetermined number of sAid drive signals in response to each output signal, said counting means providing an output at the end of each counting cycle; d. a stepping motor responsive to said drive signals for pulsatingly advancing work material into the path of said sewing needle; and e. gating means responsive to the output of said counting means for inhibiting said drive signals whereby the distance traversed by said work material for each stroke of the sewing needle is determined by the predetermined number of counted drive signals in each counting cycle.
 2. A system as defined in claim 1 further comprising: means for generating a plurality of command signals in response to a sequence of predetermined number of drive signals; and logic circuit means responsive to said command signals for selectively directing said drive signals to said stepping motor such that the direction of advancement of said work material is controlled by said command signals.
 3. A system as defined in claim 2 wherein said means for generating said command signals comprises manually adjustable electronic counting means.
 4. A sewing machine control system as defined in claim 14 further comprising, a substantially flat bed, a sliding table mounted on said flat bed, means for clamping the work material to be sewn against said sliding table and means for coupling said stepping motor to said sliding table such that said sliding table is advanced rectilinearly in response to the rotation of said stepping motor.
 5. Apparatus as defined in claim 4 wherein said clamping means is pivotally connected to one end to said sliding table for movement therewith and extends outwardly forming a flat base for biasing the work material against said sliding table, and wherein said coupling means comprises a pully and belt drive.
 6. A control system for a sewing machine including a sewing head having a sewing needle and drive means, comprising: a. means for generating a predetermined number of drive signals in response to each stroke of the sewing needle; b. a stepping motor responsive to said drive signals for pulsatingly advancing work material into the path of said sewing needle; c. a plurality of light sensitive devices arranged in a predetermined sequence; d. a light source; e. means for advancing said light source past each of said light sensitive devices; and f. gating means electrically connected to each of said light sensitive devices and responsive to the electrical state thereof for alternately changing the direction of travel of said stepping motor such that the distance traversed by said material in each direction is governed by the relative displacement between said light sensitive devices.
 7. A system as defined in claim 6 wherein said plurality of light sensitive devices comprises a first photocell representing length of pre-tack, a second photocell displaced a predetermined distance from said first photocell representing length of running tack, and a third photocell displaced a predetermined distance from said second photocell representing post-tack and wherein the position of each photocell with respect to one another is manually adjustable.
 8. A system as defined in claim 7 wherein said light sensitive devices are mounted on a panel in a remote location from said sewing machine and wherein said light source is mounted on a movable conveyor adjacent said light sensitive devices.
 9. A system as defined in claim 9 further comprising; a substantially flat bed, a sliding table mounted on said flat bed, means for clamping the work material to be sewn against said sliding table, means for coupling said stepping motor to said sliding table such that said sliding table is advanced rectilinearly in response to the rotation of said stepping motor, means for transmitting electrical signals responsive to the movement of said sliding table, and receiving means connected to said movable conveyor in said remote location for advancing said conveyor in response to the transmitted siGnals. 